坚贞不屈的英文：
[Literal Meaning]
firm/faithful/not/yield
to remain faithful and unyielding (in front of the enemy and evil forces)

[解释]
意志坚定，决不屈服。

[Explanation]
to remain faithful and unyielding

[例子]
尽管敌人严刑拷打，这个战士仍然坚贞不屈，什么都没有说。

[Example]
In spite of the enemy's torture, the soldier still remained faithful and unyielding and said nothing.

impregnable virtue
坚贞不屈的情操

Through those long years of imprisonment and torture, he remained faithful and unyielding.
在那些遭受囚禁和酷刑的漫长岁月里，他始终坚贞不屈。